Analysis Of The Thermal Lens Effect On Yb: YAG Thin-Disk Laser Crystal

Yb:YAG thin-disk laser is already one of the most popular high power solid-state lasers in recent years, as well as its good development prospects. Yb:YAG is a good laser crystals with wide absorption bandwidth, long fluorescence lifetime and high quantum efficiency. The thin-disk laser concept is a revolutionary design on the crystal geometric structure that allows realization of lasers with fast cooling, good thermal performance, high efficiency beam, high beam quality, low operating cost. These characters are the key to success for Yb:YAG thin-disk laser. But even Yb:YAG crystals will still generate heat when it is working; and the revolutionary design of thin-disk laser aslo brings some new features in the thermal lens effect. Thermal lens effect is still the problem for the development of Yb:YAG thin-disk laser. So it is necessary to detailed analysis the thermal lens effect of Yb:YAG thin-disk laser.In this thesis, the analytical solution of the Yb:YAG crystal temperature distribution is calculated, which is based on the uniform end-pumped and the uniform end-cooling model of Yb:YAG thin-disk laser. The stress and strain distribution of the Yb:YAG crystal is calculated, based on the thermal analytical solution and the theory of elastic mechanics, with the plane stress approximation. Both the thermal analytical solution and the stress and strain distribution are verified by the finite element simulation results. The optical path distance of the Yb:YAG crystal is calculated based on the temperature distribution and the strain distribution, which are already calculated. The focal length distribution of the Yb:YAG crystal is calculated with the OPD distribution, by analogy to the relationship in ideal thin lens between the focal length and the OPD as well as the analysis of thermal lens effect. This theoretical work is proved by experimental in the present conditions.